Tackling terrorists

In the world in which we live, the main terrorist threat comes not from bombs or bullets but silicon and sand.

The issue of glass as a terrorist weapon was pushed to the top of the security agenda by the attack on the Alfred P. Murrah Federal Building in Oklahoma City in 1995, the first time that a major terrorist attack happened on U.S. soil. In that attack, 167 people died and 750 were injured.

A 2007 report stated "the glass facade of the Alfred P. Murrah Federal Building in Oklahoma City shattered into thousands of heavy glass chunks that were propelled through occupied areas of the building with devastating results." Eric Lavonas, a doctor at the Department of Emergency Medicine, Carolinas Medical Center, Charlotte, N.C., and Andre Pennardt, assistant professor of Military and Emergency Medicine, Uniformed Services University of the Health Sciences, Bethesda, Md., wrote the report, available at emerg/topics63.htmwww.emedicine.com/.

After the Oklahoma bombing, the Department of Justice issued recommendations for upgrading federal building security. The 1995 release, available at http://www.usaid.gov/policy/ads/500/565a1.pdf calls for the "installation of shatter-proof glass on exterior windows."

Most people killed or badly injured in a blast involving high-order explosives (HE) are affected by either primary or secondary blast injuries. Primary HE blast injuries are caused by high-pressure gases from the explosion rapidly expanding to produce a supersonic blast wave and are generally fatal.

Secondary blast injuries, caused by flying objects including glass fragments, are more common than primary blast injuries and are the most common causes of death in blasts. The penetrating injuries occur most often in the exposed areas of the body such as the head, neck and extremities.

At Oklahoma, glass fragments were found six miles from the detonation. In New York on Sept. 11, 2001, 15,500 windows were damaged within a mile of Ground Zero, nearly 9,000 within half that distance.The Texas Tech Glass Research and Testing Laboratory estimates that approximately 75 percent of all damage and injury from bomb blasts can be attributed to flying and falling glass following an explosion. They note that a single square foot of unprotected glass can project as many as 100 sharp shards of glass flying at speeds of up to 300 feet per second.Until Oklahoma, there had been little market demand for blast mitigation glazing systems in the United States. There was a similar complacency in the United Kingdom, despite the Provisional Irish Republican Army that conducted an armed campaign throughout the U.K. from 1969 into the 1990s. Most government buildings were protected simply by blast curtains.A 1998 report written by Eugene Sevin and Richard Little for the National Academy of Engineering, Washington, D.C., helped to change official views. "A more proactive approach is to develop glazing materials that meet aesthetic and functional design objectives but do not contribute to the explosion-induced projectile hazard," the report said. It is available at http://www.nae.edu/nae/bridgecom.nsf/weblinks/NAEW-4NHMEP?Open-Document.

That report, among many others, made clear that terrorist activity might not be a transient phenomenon and had to be planned for at the design stage of a new building, particularly for sensitive commercial or military installations. And that it was up to the glass and glazing industries to come up with technical solutions.

The only immediate solution was to limit the amount of glass in the building and to frame it in an extremely obtrusive system. This wasn't the way forward for architects or the inhabitants of that building. Like others involved in specialist glazing, Wrightstyle saw a void in the market and an opportunity to provide a design solution.

If buildings were to be built like reinforced bunkers, the bad guys would have won. So we embarked on a design journey that last year brought us to a test site in Northumberland, U. K. We simulated what would happen to our glazing system if a truck packed with about 1,100 pounds of TNT-equivalent explosive was detonated nearby.

Our integrated system passed the test, remaining intact within its frame, and then passed a second test when we moved the seat of the explosion closer to the glass and simulated a car bomb attack. It was a smaller explosion but, being closer to the test rig, it generated a more intense shock wave.

The Wrightstyle SG Blast Resistant system utilizes elements from our well-established SG curtain wall system, and is semi-unitized and structurally glazed. This gives it the appearance of a non-enhanced glazing system, a key design element.

The main steel profiles are about 21Ú2 inches wide by 51Ú2 inches deep, and made from cold-rolled hollow steel. They are high strength and can hold large glass expanses. The glass, a multiple laminate sandwich with plasticised interlayers, is factory-bonded to an aluminium carrier system and fixed into place with an interlock screw and toggle system.

The SG Blast Resistant system limits deflection under positive blast load, or what happens first when a bomb goes off. The interlock toggle system prevents the glass from being pulled out under negative blast loading, or the huge drop in pressure that happens after the initial blast wave.

We consider ourselves as a specialist glass and steel company. With new threats worldwide, our systems have moved into the mainstream market. Our last two projects were a banking data center in the Far East and a control building associated with the Asian Games in Doha, Qatar.

In terms of safety and aesthetics, the system is a significant step forward. It protects inhabitants against terrorist attacks without making buildings look like reinforced bunkers. Architects can still use their full imagination to design stunning buildings.

As such systems become more regularly specified, and architects fully realize that large-span glass is once again a design option for any building, the market around the world will expand dramatically.

For video of the blast test, go to www.wrightstyle.co.uk/blasttest.